The present invention relates to a copier, facsimile apparatus, printer or similar image forming apparatus and, more particularly, to an image forming apparatus of the type having a rotary developing device.
An image forming apparatus having a rotary developing device, or revolver as generally referred to, is disclosed in Japanese Patent laid-Open Publication Nos. 62-25 1772 and 63-78170 and Japanese Utility Model laid-Open Publication No. 63-41164 by way of example. The revolver is made up of a rotary developing unit, a rotary toner storing unit, and toner toner conveying means. The developing unit is rotatable in the vicinity of an image carrier in the form of a photoconductive drum and has a plurality of developing sections or chambers thereinside. The storing unit is coaxially provided on one end of the developing unit. A plurality of storing chambers are defined in the storing unit in one-to-one correspondence with the developing chambers, and each stores toner of particular color. Each storing chamber is communicated to one of the developing chambers by the conveying means.
The developing chambers and storing chambers are related such that the conveying means exists, when the associated developing chamber is located at a developing position where it faces the image carrier, at a position in the respective storing chamber where the toner gathers due to its own weight, e.g., at a lower portion of the storing chamber. The conveying means suitably replenishes fresh toner from the storing chamber into the developing chamber in which either a one-component type developer, or toner, or a two-component type developer, or toner and carrier mixture, is present. When the storing chamber runs out of the toner, toner must be replenished into the chamber from the outside. To save time and labor for the replenishment, the storing chamber should preferably be implemented as a toner container or cartridge removably mounted to the developing unit. Then, a container run out of toner will be readily replaced with a new toner container full of fresh toner. Laid-Open Publication No. 63-41164 mentioned earlier teaches a plurality of toner containers removably mounted to the developing unit.
When the containers are removably mounted to the developing unit, it is not desirable that the conveying means, protruding from the developing chambers toward the containers be left bare. Preferably, there are provided toner inlet portions surrounding the conveying means. The inlet portions are each provided with an inlet corresponding to the outlet of the associated container. The inlet portions are communicated to the respective developing chambers. This kind of configuration prevents the operator from touching the conveying means which would smear the operator's hands and cloths. The containers, inlet portions and developing chambers should preferably be related such that when one developing chamber is located at the developing position, the toner stored in the associated container flows into the inlet due to its own weight, and such that the conveying means exists in the inlet portion at a position where the incoming toner is present.
However, it is sometimes impossible to guarantee a space great enough to accommodate a plurality of containers for layout reasons and, therefore, to combine the containers and developing chambers in the relation stated above. Then, priority must be given to the relation between the developing chambers and the inlet portions which directly contribute to the replenishment of toner; that is, the preferable relation between the containers and the inlet portions must be sacrificed. More specifically, to allow the toner conveying means to exist, when the developing chamber is held at the developing position, at the position in the inlet portion where the toner is present, the toner in the container cannot flow into the inlet portion despite its own weight. Hence, when one developing chamber is held at the developing position to effect image formation continuously, the replenishment of toner into the chamber fails as soon as the toner in the inlet portion is fully consumed.
The above problem also occurs with a developing device having a single developing chamber and a single toner container, so long as it is a rotary developing device. Further, assume that the container is not located on an axis extending out from one side of the developing chamber, but it is located radially inwardly or outwardly of the chamber, and that the toner is directly supplied from the container to the chamber without the intermediary of the conveying means. Even this kind of scheme will have the same problem if an arrangement is so made as to allow the toner to be fed from the container to the chamber only when the outlet of the container and the inlet of the chamber lie in a predetermined angular range.
The container may be longer at one end than the other end where the outlet is present, and may be so configured as to move the toner existing at the one end toward the outlet due to the rotation of the developing unit. However, after the toner around the outlet has been replenished into the developing chamber, the remaining toner cannot be fed into the chamber unless the developing unit rotates.
Even when direct or indirect sensing means determines that the container has run out of the toner, the toner often remains cohered around the outlet of the container. If the container with the cohered toner is pulled out of the developing unit, the toner drops from the outlet and contaminates the surrounding. In addition, this is not desirable in the aspect of the effective use of toner.
Because the containers differ from each other as to the time when they run out of toner, they should preferably be replaceable independently of each other. In such a case, although the empty state of a container (referred to as a near end condition hereinafter) may be displayed on the operation panel of the apparatus, it is difficult for the operator to identify the empty toner. For example, the operator must pull out the containers one by one and feel their weights.
A mount portion for mounting the container is included in the revolver body, i.e., in the developing chamber itself or in a portion communicated to the chamber. The relation between the inlet formed in the mount portion and the outlet of the container in the up-and-down direction changes with a change in the angular position of the revolver, i.e., the position of the container. Therefore, when the containers are replaceable independently of each other and if one of the containers is pulled out, while the toner is present in the inlet of the chamber, at an angular position where the inlet is disposed above he outlet of the container, the toner in and around the inlet drops and contaminates the surrounding.
Moreover, assume that the configuration of the outlet of the container is apt to gather the toner therearound. Then, if the container is pulled out at an angular position where the outlet of the container is disposed above the inlet of the chamber, the toner also drops from the outlet of the container.